1. Field of the Invention
The present invention relates to a novel, useful polymerization catalyst and a process for producing a polymer using the polymerization catalyst. More particularly, the present invention relates to a polymerization catalyst especially useful as an olefin polymerization catalyst, and a process for producing an olefin based polymer, using the polymerization catalyst.
2. Related Art
Heretofore, as highly active homogeneous olefin polymerization catalysts, those catalysts composed of a transition metal compound and aluminoxane are known (Japanese Patent Application Unexamined Publications Nos. Sho 58-19309 and 60-217209).
Further, it has been proposed that as active species of the homogeneous olefin polymerization catalysts, cation species are useful [J. Am. Chem. Soc. 81, 81 (1959), J. Am. Chem. Soc. 82, 1953 (1960), J. Am. Chem. Soc. 107, 7219 (1985)]. The use of the active species in olefin polymerization after isolation, is described in, for example, J. Am. Chem. Soc. 108, 7410 (1986), Japanese Patent Application PCT publication No. Hei 01-502636, Japanese Patent Application Unexamined Publication No. Hei 03-139504, and European Patent Publication No. 468651. The use of the active species with an organoaluminum compound is described in, for example, Japanese Patent Application Unexamined Publication No. Hei 03-207704 and International Patent Publication No. 92-1723. Further, an olefin polymerization catalyst composed of a transition metal compound having a ligand containing a group, --SO.sub.3 R and an organoaluminum oxy compound is described in, for example, European Patent Publication No. 519746.
However, the catalyst system composed of a combination of a transition metal compound and aluminoxane have some disadvantages. For example, trimethylaluminum which is a synthesis material for aluminoxane is flammable and explosive, and thus its handling is dangerous. Also, trimethylaluminum is expensive. Further, a large amount, against a transition metal compound, of aluminoxane should be used. Therefore, the catalyst systems are not effective in industrial productivity.
Further, in any examples of polymerization disclosed in the above publications or literature, monocation species are used as an active species. Thus, these catalysts are not always satisfactory in view of the catalytic activities for olefin polymerization and the molecular weight of the resultant polymer.
The present invention was made in view of the above problems, and has its object of providing a highly active polymerization catalyst which can give rise to resultant homo- or co-polymers having high molecular weight and having a narrow comonomer distribution, and make it possible to control the molecular weight distribution within narrow range, and a process for producing a polymer using the polymerization catalyst.